An in-class exercise to demonstrate how to setup a many-to-many relationship between Movies and Actors.

Here's a log of the steps I took:

• npm init
• npm install --save express pg sequelize sequelize-cli
• add node_modules/ to .gitignore
• sqlize init
• modify config.json to use postgres
• sqlize model:create --name Actor --attributes name:string
• sqlize model:create --name Movie --attributes title:string
• make sure Postgres.app is running!
• createdb movies_and_actors_dev
• sqlize db:migrate
• Actor.hasMany(models.Movie)
• Movie.hasMany(models.Actor)
• Possibly unhandled SequelizeDatabaseError: error: relation "ActorsMovies" does not exist
• sqlize model:create --name ActorsMovies --attributes ActorId:string,MovieId:string
• sqlize db:migrate

Oops, I realized I made a mistake. ActorId and MovieId should have been integers, not strings. Now I'm going to reset the database, modify my ActorsMovies migration and model files, and then rerun all the migrations.

• sqlize db:migrate:undo // undo all the migrations
• movies_and_actors_dev=# DROP TABLE "SequelizeMeta"; // overcome bug in sequelize
• change DataTypes.STRING to DataTypes.INTEGER for ActorId and MovieId in actors-movies migration file.
• change DataTypes.STRING to DataTypes.INTEGER for ActorId and MovieId in actorsmovies.js model file.
• sqlize db:migrate // redo all the migrations

Things seems to work now. I am able to create Actors and Movies and associate them in a many-to-many relationship.

However, I notice that I am able to delete an Actor which will leave ophaned entries in the ActorsMovies table. Foreign key contraints are supposed to help us here. We never labeled anything as a foreign key, so let's fix that.

• sqlize db:migrate:undo
• movies_and_actors_dev=# DROP TABLE "SequelizeMeta";
• in actors-movies migration file:
  • ActorId references "Actors" and referencesKey "id"
  • MovieId references "Movies" and referencesKey "id"
• sqlize db:migrate